Here we can change the variables to real numbers, just to make things easier for us. For the sake of calculation, let’s say that x=10, y=6, and z=1.
So, y years from now, Yann will be x years old. If we plug in our randomly chosen numbers, we get that Yann will be 10 years old 6 years from now. This means that today, he would be x-y years old, or 10-6, so 4 years old today.
Next we ask how old he was z years ago, or in this case, 1 year ago. We know that if you’re 4 years old now, you were 3 years old last year. In other words, you’re 4-1 years old, or x-y-z years old.
Your answer is x-y-z.
Start by multiplying the 9 out:
9(-6 + 8y) = -54 + 72y
Then, add the 7:
-54 + 72y + 7
Then simplify the whole thing:
-47 + 72y
A^4 * a^6
exponent rule : x^y * x^z = x^(y + z)
so, a^4 * a^6 = a^(4 + 6) = a^10
